Outside the palace, a band of guardsmen in scarlet tunics and bearskin hats played "Happy Birthday" during the Changing of the Guard ceremony.

And at the centuries-old Tower of London, there was a second salute with 62 guns.

The queen is Britain's oldest and longest-reigning monarch, having become queen on Feb. 6, 1952. She is also the world's longest-reigning living monarch since the death of Thailand's King Bhumibol Adulyadej last year.

Elizabeth also has an official birthday, marked in June — when the British weather is better — with the "Trooping the Color" military parade.

Here's a look at some more milestones and numbers related to the queen:

Elizabeth has reigned for 65 years and 75 days. On September 9, 2015, she became Britain's longest-reigning monarch, passing her great-great-grandmother Queen Victoria.

She has had 13 British prime ministers serve during her reign, from Winston Churchill to Theresa May.

She has met 12 U.S. presidents, from Herbert Hoover (after he left office) to Barack Obama, more than a quarter of all the U.S. presidents since Independence. She is due to host President Donald Trump for a state visit later this year.

She has traveled more than 1 million miles (1.6 million kilometers) on official trips, visiting 106 countries.

She has visited Canada 22 times —the largest number of trips to any nation.

She has four children, eight grandchildren and five great-grandchildren.

She has cut back on her official duties in the last few years, but Elizabeth still conducted 332 official engagements in 2016.

Britain Celebrates Queen Elizabeth's 90th Birthday

Queen Elizabeth and her family marked the monarch's official 90th birthday with a parade, a colorful military ceremony and an appearance at Buckingham Palace in London, United Kingdom, on Saturday.